posted 14 years ago
I don't know the specifics of the AJAX library, but in the days before AJAX, I was part of a team that did something similar. We created a separate frame (iframe) which was not visible. We then posted requests to our back-end server using this frame, then applied the results to our page using JavaScript. This allowed us to update the page data without posting and redrawing the entire page.
I would expect that the AJAX library is doing something similar, although I doubt they use a hidden iframe.